US20210317483A1

US20210317483A1 - Recombinant microorganism and method for producing 1,5-diaminopentane

Info

Publication number: US20210317483A1
Application number: US17/062,783
Authority: US
Inventors: Jo-Shu Chang; I-Son NG; Shih-Fang Huang; Hong-Yi Lin; Sheng-Feng Li; Chia-Wei Tsai; Chih-Yu Huang; Wan-Wen Ting
Original assignee: China Petrochemical Development Corp
Current assignee: China Petrochemical Development Corp
Priority date: 2020-04-14
Filing date: 2020-10-05
Publication date: 2021-10-14
Anticipated expiration: 2040-10-05
Also published as: TWI748408B; CN113528561B; US11408015B2; TW202138563A; CN113528561A

Abstract

Provided is an expression vector including a nucleotide sequence for encoding lysine decarboxylase CadA, and a sequence of a constitutive promoter for regulating the expression of the nucleotide sequence. Also provided is a recombinant microorganism including the expression vector and a method of producing 1,5-diaminopentane by using the recombinant microorganism.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims foreign priority under 35 U.S.C. § 119(a) to Patent Application No, 109112489 filed on Apr. 14, 2020, in the Intellectual Property Office of Ministry of Economic Affairs, Republic of China (Taiwan, R.O.C.), the entire content of which is incorporated herein by reference.

REFERENCE TO SEQUENCE LISTING

This application contains a Sequence Listing in computer readable form, which has been submitted electronically via EFS-web in ASCII format. Said ASCII copy, created on Oct. 2, 2020, is named Seq_Listing_123710_06401 and is 15,334 bytes in size. The computer readable form of the sequence listing is part of the specification or is otherwise incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a microorganism for producing 1,5-diaminopentane, and in particular to a recombinant microorganism and a method for producing 1,5-diaminopentane.

2. Description of the Related Art

1,5-diaminopentane is an important monomer for the synthesis of polymers such as polyamide (i.e., nylon). The existing methods for producing 1,5-diaminopentane by microorganisms can be roughly divided into three types: (1) the method of microbial metabolism in vivo; (2) the co-culture method, in which two microorganisms are co-cultured, and the product of one of the two microorganisms is used as a substrate for the other microorganism; and (3) whole-cell bioconversion in vitro, in which a whole biological organism is uses as a catalyst for chemical conversion; that is, the microorganism is cultured to a certain cell amount, and then a substrate is added for catalysis and conversion to a product.
Microorganisms that can be used to produce 1,5-diaminopentane include Escherichia coli (E. coli), which can express lysine decarboxylase, CadA, and catalyze the conversion of lysine to produce diaminopentane. Studies on the production of diaminopentane through the microbial metabolism include: the method comprising using glucose as a carbon source, and after removing the genes for product metabolism, expressing CadA by a low copy number vector p15A containing Tac promoter, in which the highest yield is only 9.6 g/L [1]; and the method comprising using galactose as a carbon source and expressing CadA by a high copy number vector pETDuet, in which the highest yield is only 8.8 g/L [2]. From the above two examples, the high-yield diaminopentane cannot be obtained by regulating the metabolic pathway of E. coli. The possible reason is that since the cells produce substrates and products at the same time, it leads to a slow production rate of the products.
In 2018, Wang et al. used co-culture to generate substrates and products by individual strains, and the two strains used different carbon sources (the former used glucose, while the latter used glycerol). Without competing with each other, the final yield can reach 28.5 g/L after 50 hours of fermentation [3]. The co-culture method can indeed increase yield; in terms of time efficiency, however, the yield is still unsatisfactory.
The whole-cell bioconversion approach provides an alternative solution, which comprises increasing the amount of bacteria and accumulating the amount of enzymes through high-density fermentation, and then catalyzing the conversion of lysine to 1,5-diaminopentane (DAP, also known as cadaverine). In 2014, Weichao Ma et al. used the pETDuet expression system to simultaneously express CadA and cadaverine/lysine antiporter (CadB). After catalysis with cells in an amount of 8 g/L for 16 hours, the maximum yield can reach 221 g/L [4]. In addition, in 2015, Kim et al. used pET24m to express CadA. As a result, the enzyme activity was 30.27 mmol/cell dry weight (mg)/min, and after 2 hours of catalysis, the final yield was 142.8 g/L [5].
Moreover, CN Patent Publication No. 105316270 discloses that the CadA gene and the CadB gene containing RBS22 are inserted into the pET28a (+) vector, and an E. coli strain B is used as a host. CN Patent Publication No. 104498519 also discloses that pETDuet is used as a vector to express CadA and CadB, wherein 5′ end of CadB is fused with a periplasmic pectate lyase (pelB) leader sequence. Furthermore, EP Patent Publication No. 1482055 discloses that CadA is constructed into pUC18 vector, and an E. coli strain K-12 JM109 is used as a host.
However, the existing whole-cell bioconversion for producing 1,5-diaminopentane, including the above-mentioned methods of whole-cell bioconversion, mostly employ the E. coli T7 expression system, which must be added with expensive inducers such as isopropyl β-d-1-thiogalactopyranoside (IPTG) for culture. Also, since the induction time and the required concentration of the inducer need to be precisely controlled, it is very unfavorable for the production of whole-cell enzymes in high quantities. In addition, since E. coli BL21 (DE3) as a host in the T7 system has poor tolerance to its own product, i.e., 1,5-diaminopentane, the production of 1,5-diaminopentane is thus limited as well.
In view of the foregoing, it is necessary to provide a method that can effectively increase the production capacity of 1,5-diaminopentane to solve the existing problems in the conventional technology.

SUMMARY OF THE DISCLOSURE

In order to solve the above-mentioned problems, the present disclosure provides an expression vector, comprising a nucleotide sequence for encoding lysine decarboxylase CadA and a sequence of a constitutive promoter for regulating expression of the nucleotide sequence.
In an embodiment, the nucleotide sequence for encoding lysine decarboxylase CadA is a sequence having at least 80% identity to SEQ ID NO: 1 and having the same activity as SEQ ID NO: 1. For example, the nucleotide sequence encodes a protein having lysine decarboxylase activity. In another embodiment, the lysine decarboxylase CadA has an amino acid sequence of SEQ ID NO: 2 or an amino acid sequence of SEQ ID NO: 2 with a conservative substitution.
In an embodiment, the constitutive promoter is one of J series constitutive promoters. In another embodiment, the J series constitutive promoters include promoters J23100, J23101, J23102, J23103, J23104, J23105, J23106, J23107, J23108, J23109, J23110, J23111, J23112, J23113, J23114, J23115, J23116, J23117, J23118 and J23119. In yet another embodiment, the constitutive promoter is J23100, J23109 or J23114.
In an embodiment, the constitutive promoter has a sequence having at least 80% identity to SEQ ID NO: 3 and has the same activity as SEQ ID NO: 3. For example, the constitutive promoter has a sequence that is capable of being a constitutive promoter.
In an embodiment, the expression vector has a sequence having at least 80% identity to SEQ ID NO: 4 and has the same activity as SEQ ID NO: 4.
The present disclosure also provides a recombinant microorganism comprising the expression vector as described above, which may be used to produce 1,5-diaminopentane.
In an embodiment, the microorganism is genus Escherichia, Klebsiella, Erwinia, Serratia, Providence, Corynebacterium or Brevibacterium. In another embodiment, the microorganism is Escherichia coli. In yet another embodiment, the microorganism is E. coli strain K-12 W3110. In an embodiment, the recombinant microorganism provided by the present disclosure is Escherichia coli W3110-JcadA, which is a strain deposited at Bioresource Collection and Research Center (BCRC) of the Food Industry Research and Development Institute under BCRC Accession No. BCRC 940690 on Dec. 19, 2019, and also deposited at Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures under DSMZ Accession No. DSMZ 33576 on Jul. 15, 2020.
The present disclosure also provides a method for producing 1,5-diaminopentane, comprising: mixing the above-mentioned microorganism with lysine in a solution to convert the lysine to 1,5-diaminopentane; and recovering the 1,5-diaminopentane from the solution.
In an embodiment, the method further comprises culturing the above-mentioned microorganism in a medium. In another embodiment, the culture of the microorganism is performed by high-density fermentation. In yet another embodiment, the culture of the microorganism is performed before the microorganism and lysine are mixed in the solution.
In an embodiment, the concentration of the microorganism mixed with lysine in the solution is 1 to 6 of an optical density measured at a wavelength of 600 nm (OD₆₀₀). In another embodiment, the concentration of the lysine in the solution is 1 M to 2 M. In yet another embodiment, the concentration of the lysine in the solution is 1 M, 1.2 M, 1.4 M, 1.5 M, 1.6 M, 1.8 M or 2 M.
In an embodiment, the solution has a pH value of 4 to 8. In another embodiment, the pH value of the solution is 4, 4.5, 5, 5.5, 6, 6.5, 6.8, 7, 7.5 or 8.
In an embodiment, the method further comprises adding a cofactor to the solution, wherein the concentration of the cofactor in the solution is 0.01 mM to 0.05 mM. In another embodiment, the concentration of the cofactor in the solution is 0.01 mM, 0.02 mM, 0.03 mM, 0.04 mM, or 0.05 mM. In yet another embodiment, the cofactor is pyridoxal-5′-phosphate (PLP).
The present disclosure utilizes a non-inducible expression system to express lysine decarboxylase CadA in a microbial host as a whole-cell biocatalyst, which provides, e.g., high protein expression, high enzyme activity and slow degradation rate, such that the catalytic efficiency of diaminopentane of microorganisms may be significantly improved. In addition, the whole-cell biocatalyst is capable to produce 1,5-diaminopentane without an additional inducer, and thus the cost of producing 1,5-diaminopentane is reduced and the production process is simplified, thereby enhancing the production capacity and yield of diaminopentane, and realizing the large-scale production of 1,5-diaminopentane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of the gene map of constitutive expression plasmid pSU-J23100-CadA. P_J23100: J23100 promoter; B0034 RBS: ribosome binding site; CadA: lysine decarboxylase CadA gene; pUC: origin of replication of plasmid pSU; CmR: chloramphenicol acetyltransferase gene; HindIII and BglII: restriction sites.

FIG. 1B shows the result of DNA electrophoresis of the plasmid pSU-J23100-CadA, indicating that the plasmid has a total length of about 4000 base pairs (bp), which is consistent with that shown in FIG. 1A. Molecular weight markers 3k, 4k, and 5k represent 3000, 4000, and 5000 bp, respectively.

FIG. 2 shows the tolerance of three E. coli strains to diaminopentane. BL21, W3110, MG1655: three E. coli strains BL21, K12 W3110 and MG1655; “+”: the medium containing diaminopentane; “−”: the medium not containing diaminopentane.

FIG. 3 shows the protein expression of the transformed strains after culture for 12 hours. WT: wild type W3110; JCadA: transformed strain JCadA/W3110. The unit of molecular weight marker is kDa.

FIG. 4 shows the results of whole-cell catalytic production of the transformed strain JCadA/W3110. Hour 0 is the starting point for adding 1 M substrate (i.e., lysine) and 0.05 mM cofactor (i.e., PLP). W3110: wild type W3110.

FIG. 5 shows the growth and activity of the constitutive strain and the inducible strain within 30 hours. The constitutive strain is JCadA/W3110 and the inducible strain is E. coli T7cadA/BL21 (DE3). Hour 0 is the starting point for inducing E. coli BL21 (DE3)-T7cadA with IPTG. DCW: dry cell weight.

FIGS. 6A and 6B respectively show the plasmid copy number and the protein expression (indicated by arrows) of different generations of transformed strain JCadA/W3110 cultured for 12 hours. The unit of molecular weight marker is kDa.

FIGS. 6C and 6D show the plasmid copy number and the protein expression of the transformed strain JCadA/W3110 cultured in different resistance environments for 12 hours, respectively. PCN: plasma copy number.

FIG. 7 shows the yield and activity of whole-cell biocatalysts produced by different culture methods.

FIG. 8 shows the days and activity of whole-cell biocatalyst cryopreservation at −80° C.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The detailed description of the present disclosure is described by the embodiments below. Those skilled in the art can easily understand the advantages and effects of the present disclosure from the contents disclosed in this specification. The present disclosure can also be implemented or applied by other different embodiments. The details in this specification can also be modified and changed based on different viewpoints and applications, without departing from the scope of the present disclosure. In addition, all ranges and numerical values herein are inclusive and combinable. Any value or point that falls within the range described herein, such as any integer, can be used as the minimum or maximum value to derive the subordinate range.
Unless otherwise stated in the text, the singular forms “a,” “an” and “the” used in the specification and the appended claims include plural individuals.
Unless otherwise stated in the text, the term “or” used in the scope of the specification and the attached claims includes the meaning of “and/or.”
The present disclosure provides an expression vector, which includes a nucleotide sequence for encoding lysine decarboxylase CadA and a sequence of a constitutive promoter for regulating expression of the nucleic acid molecule encoding the lysine decarboxylase. The present disclosure also provides a recombinant microorganism containing the expression vector and a method for producing 1,5-diaminopentane using the microorganism.
As used herein, the term “lysine decarboxylase” refers to an enzyme that participates in the biotechnological production of 1,5-diaminopentane in an organism, including two types of lysine decarboxylase, i.e., lysine decarboxylase 1 (CadA) and lysine decarboxylase 2 (LdcC). CadA is an inducible enzyme that may be induced by oxygen starvation, excessive lysine supply, and pH changes, whereas LdcC is a constitutive enzyme, which is independent of an external change in pH [6].
According to one embodiment of the present disclosure, the nucleotide sequence for encoding lysine decarboxylase CadA is a sequence having at least 80% (e.g., at least 82%, at least 85%, at least 90%, at least 95%, at least 98%, or at least 100%) identity to SEQ ID NO: 1, and having the same activity as SEQ ID NO: 1, such as a sequence that may encode a protein having lysine decarboxylase activity. In another embodiment, the lysine decarboxylase CadA has an amino acid sequence of SEQ ID NO: 2 or an amino acid sequence of SEQ ID NO: 2 with a conservative substitution.
As used herein, the term “sequence identity percentage” means the extent that amino acid or nucleotide residues of a candidate protein or nucleic acid fragment are identical to amino acid or nucleotide residues of a reference protein or nucleic acid fragment. When performing the above-mentioned comparison, the candidate protein or nucleic acid fragment and the reference protein or nucleic acid fragment are aligned, and gaps may be introduced as necessary, so as to form the highest sequence identity between the two sequences. When calculating the identity, the amino acid residue where is conservative substitution is regarded as different residue; the nucleotide residues which are degenerate codons are also regarded as different residues. For example, as to the codons AAU and AAC that both encode aspartic acid, it is considered that there is a different residue U or C between such two codons.
It should be understood that, compared to the amino acid or nucleotide sequence of the reference protein or nucleic acid fragment in the present disclosure, amino acid or nucleotide sequence of candidate protein or nucleic acid fragment with a modification (e.g., deletion, substitution, or addition) in at least a portion of the sequence is also within the scope of the present disclosure, as long as the resulting candidate protein or nucleic acid fragment has substantially the same biological activity as the amino acid or nucleotide of the reference protein or nucleic acid fragment. This results from the codon degeneracy. For example, in the nucleotide sequence for encoding CadA of the present disclosure, various modifications can be made in the coding region, provided that it does not change the activity of the polypeptide expressed from the coding region. Therefore, the nucleotide sequence for encoding CadA of the present disclosure may be a nucleotide sequence having SEQ ID NO: 1 or any nucleotide sequence having at least 80% identity to SEQ ID NO: 1, as long as the protein encoded by the nucleotide sequence exhibits CadA activity. For the same reasons, CadA of the present disclosure may have the amino acid sequence of SEQ ID NO: 2 or be a protein that is homologous to SEQ ID NO: 2, as long as the protein substantially exhibits CadA activity.
As used herein, the term “constitutive promoter” refers to a promoter that maintains constitutive activity in most of or in all tissues. Compared with an inducible promoter, which must be regulated by external signals or inducers, the constitutive promoter can continuously express a specific gene.
The suitable constitutive promoters for the present disclosure include those belonging to the J series constitutive promoters, for example, J23100, J23101, J23102, J23103, J23104, J23105, J23106, J23107, J23108, J23109, J23110, J23111, J23112, J23113, J23114, J23115, J23116, J23117, J23118 and J23119. In an embodiment, the constitutive promoter used in the present disclosure may be J23100, J23109 or J23114. In another embodiment, the constitutive promoter has the sequence of SEQ ID NO: 3 or at least 80% (e.g., at least 82%, at least 85%, at least 90%, at least 95%, at least 98% or at least 100%) identity to SEQ ID NO: 3, and has the same activity as SEQ ID NO: 3; for example, the constitutive promoter has a sequence that can be used as a constitutive promoter.
According to one embodiment of the present disclosure, the expression vector of the present disclosure further includes at least one selected from the group consisting of a marker gene sequence, a reporter gene sequence, an antibiotic resistance gene sequence, a restriction enzyme cleavage position sequence, a polyadenylation position sequence, an enhancer subsequence, a terminal subsequence and a regulator subsequence. In another embodiment, the expression vector has the sequence of SEQ ID NO: 4 or a sequence having at least 80% (e.g., at least 82%, at least 85%, at least 90%, at least 95%, at least 98% or at least 100%) identity to SEQ ID NO: 4 and having the same activity as SEQ ID NO: 4.
As used herein, the term “recombination” refers to artificially combining two separate sequence fragments. In general, the term “recombination” refers to a nucleic acid, a protein or a microorganism containing genetic materials derived from multiple different sources, or being encoded by genetic materials derived from multiple different sources, such as two or more organisms of different strains or species.
As used herein, the term “microorganism” refers to microscopic organism, including bacteria, archaea, viruses, or fungi. As used herein, the term “microorganism” should be interpreted to encompass the “bacteria.”
Microbial hosts suitable for the expression vector of the present disclosure include, but are not limited to, microorganisms being genus Escherichia, Klebsiella, Erwinia, Serratia, Providencia, Corynebacterium or Brevibacterium. In an embodiment, the microbial host used in the present disclosure can express the lysine decarboxylase CadA in vivo. In another embodiment, the microbial host used in the present disclosure not only expresses the lysine decarboxylase CadA in vivo, but also has tolerance to diaminopentane.
According to one embodiment of the present disclosure, the method for producing 1,5-diaminopentane of the present disclosure includes culturing the above-mentioned microbial host in a medium under a condition sufficient to produce lysine decarboxylase CadA. In an embodiment, the medium may be LB medium. In another embodiment, the method includes culturing the microorganism by high-density fermentation.
According to one embodiment of the present disclosure, the method further includes adjusting the concentration of the cultured microorganism to OD ₆₀₀1 to 6, and then mixing the microorganism with lysine in a solution.
According to one embodiment of the present disclosure, the lysine concentration in the solution is 1 M to 2 M. According to another embodiment of the present disclosure, the pH value of the solution may be 4 to 8.
According to one embodiment of the present disclosure, the solution may further contain a cofactor at a concentration of 0.01 mM to 0.05 mM.
As used herein, the term “cofactor” includes a non-protein compound that is required for an enzyme to be catalytically active. The compound may be organic or inorganic. For example, the cofactors suitable for the present disclosure include, but are not limited to, pyridoxal-5′-phosphate (PLP).
Many examples have been used to illustrate the present disclosure. The examples below should not be taken as a limit to the scope of the present disclosure.

EXAMPLES

Materials:

Sodium chloride was purchased from Sigma Aldrich Co. (USA). Yeast extract was purchased from Oxoid (Taiwan). Trypsin was purchased from Cyrusbioscience (Taiwan). Agar was purchased from BD Difco dehydration medium (France). Agarose was purchased from GeneDireX (Taiwan). Pyridoxal-5′-phosphate (PLP), diethyl ethoxymethylenemalonate (DEEMM) and sodium acetate were purchased from Sigma Aldrich Co. (USA). L-lysine hydrochloride was purchased from Cyrusbioscience (Taiwan). D(+)-glucose was purchased from Comieco (Italy). Potassium dihydrogen phosphate and dipotassium hydrogen phosphate were purchased from Showa Chemical Industry Co. (Japan). Acetonitrile used for HPLC analysis was purchased from Spectrum Chemical Manufacturing Corp. (USA). The PCR reagent Ex-Tag was purchased from Takara Bio Inc. (USA). Restriction enzymes were purchased from New England Biolabs (USA). T4 DNA ligase was purchased from Leadgene Co., Ltd. (Korea). The primers were synthesized by Integrated DNA Technologies (USA).

Example 1: Construction of Recombinant Expression Vector

With using the genome of E. coli K-12 MG1655 as a template, primers HindIII-CadA-F (5′-GCA AGC TTA TGA ACG TTA TTG CAA TAT TGA ATC AC-3′ (SEQ ID NO: 5)) and BglII-CadA-R (5′-GCA GAT CTT CAT TTT TTG CTT TCT TTC AAT ACC TTA ACG GTA TAG CGG CC-3′ (SEQ ID NO: 6)) were synthesized for polymerase chain reaction (PCR).
The PCR was used to amplify specific DNA sequence fragments. The required materials included DNA template, 5′-end primer, 3′-end primer, deoxynucleotide triphosphate (dNTP), 10× polymerase buffer, and polymerase. The polymerase used in this example included Ex-Taq. The PCR product was analyzed by DNA electrophoresis and recovered by tapping, so as to obtain the amplified lysine decarboxylase CadA fragment.
The amplified CadA fragment was digested with HindIII and BglII, and then the CadA fragment was inserted into the pSU-J23100 vector to construct plasmid pSU-J23100-CadA. As shown in FIG. 1A, the plasmid contains a constitutive promoter J23100 (Accession No.: LP934757), a ribosome binding site B0034RBS (Biobrick No. BBa B0034), and CadA gene regulated by the promoter J23100.
For transformation, commercially available DH5a competent cells were added with about 10 μL of plasmid pSU-J23100-CadA. The mixture was left on ice for 30 minutes, further put in a water bath at 42° C. for 1.5 minutes, and then put on ice for 10 minutes. Next, after adding 400 μL of LB liquid medium or SOC (super optimal broth with catabolites repression) medium, the mixture was shaken in an incubator at 37° C. for about 60 to 90 minutes, and then was subject to centrifuge at 4000 rpm for 3 minutes. After removing 300 μL of supernatant, all competent cells containing recombinant DNA were coated on solid medium containing antibiotics, and cultured overnight at 37° C.
Several colonies generated on this solid medium were selected and inoculated into liquid medium in a test tube containing antibiotics, and cultured overnight in an incubator at 37° C. The next day, 2 mL of bacterial solution was taken from the medium for plasmid extraction. The extracted plasmids were then verified by restriction enzyme cleavage. The plasmid pSU-J23100-CadA had a total length of 4267 bp, which was consistent with the DNA electrophoresis result shown in FIG. 1B (i.e., the fragment indicated by the arrow), implying that the CadA gene was successfully constructed in pSU vector.

Example 2: Expression Host Test

In order to select microorganisms with better tolerance to diaminopentane as the expression host, three common E. coli strains were selected: BL21, K-12 W3110 and MG1655.
First, the three strains were individually cultured for 2 hours, and then 0.2 M of diaminopentane was added to the medium of the three strains. As shown in FIG. 2, without the addition of diaminopentane, W3110 and MG1655 grew faster than BL21; while after the addition of diaminopentane, the growth rates of the three strains were all delayed, and the bacterial numbers were all decreased. However, W3110 has the fastest growth rate and the least decrease in the period of 4 to 12 hours, and thus was considered as having higher tolerance to pentadiamine. Therefore, E. coli strain K-12 W3110 was subsequently selected as the expression host.

Example 3: Preparation of Recombinant Microorganisms

The plasmid pSU-J23100-CadA prepared in Example 1 and stored in the selected host E. coli DH5a was subjected to plasmid extraction and transformed into E. coli strain K-12 W3110. The protein expression was analyzed after 12 hours of culture, in which wild-type W3110 was taken as a control.
As shown in FIG. 3, the transformed strain JCadA (hereinafter also referred to as JCadA/W3110 or W3110-JCadA) has a higher CadA expression level (i.e., the fragment indicated by the arrow) than the wild-type W3110 (WT).
The E. coli transformed strain W3110-JCadA has been deposited under Budapest Treaty at Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures (Inhoffenstr. 7 B, D-38124 Braunschweig, Germany) on Jul. 15, 2020 and has been given the DSMZ Accession No. DSM 33576 by the International Depositary Authority. This biological material was subjected to the viability test and passed.

Example 4: Activity Test of Recombinant Microorganisms

The transgenic strain JCadA/W3110 of Example 3 was cultured and then centrifuged at 10,000 rpm for 10 minutes. The cell pellet was then suspended in deionized water, and the optical density of the bacterial solution at 600 nm wavelength (OD₆₀₀) was adjusted to reach 6 (OD₆₀₀=6). Next, the mixture was added in a solution containing 1 M of lysine as a substrate and 0.05 mM of pyridoxal-5′-phosphate (PLP) as a cofactor, and placed in an incubator with oscillation for reaction (35° C., 200 rpm). During the reaction, the contents of the remaining lysine and diaminopentane produced in the solution were confirmed.
As shown in FIG. 4, by using the transgenic strain JCadA/W3110 as a whole-cell biocatalyst, as the catalytic reaction time increases, the content of lysine decreases, and the content of diaminopentane increases, indicating that the transformed strain JCadA/W3110 can catalyze the bioconversion of lysine to diaminopentane. In contrast to the wild-type W3110, the residual amount of lysine was only slightly reduced, and no diaminopentane was produced. It can be seen that a whole-cell biocatalyst using the constitutive expression system indeed exhibits more CadA activity than the wild-type W3110, and can quickly catalyze the production of 1,5-diaminopentane in vitro.

Example 5: Comparison of Yield and Activity of Inducible and Constitutive Microbial Systems

In order to compare the CadA activity of the strains with the constitutive expression system and the inducible expression system, JCadA/W3110 (constitutive strain) and T7cadA/BL21 (DE3) (inducible strain) were individually cultured in LB medium in 5 L fermentation tanks (FB-6S, FIRSTEK, Taiwan) under the same conditions, and the bacterial growth number and activity within 33 hours of culture were recorded. The conditions of the fermentation tank were as follows: dissolved oxygen (DO) 10 to 30%, air flow rate 1.5 vvm, pH=6.8, 32° C., and 100 rpm. IPTG inducer was additionally added to the medium of T7cadA/BL21 (DE3) in a concentration of 0.00167 g/L. The number of bacteria was represented by the OD value which was measured with a spectrophotometer at a wavelength of 600 nm, and the activity of lysine decarboxylase CadA was measured with BP assay.
The process of BP assay was briefly described as follows:
First, the bacterial mass was quantified to OD₆₀₀=5, and then high-pressure disruption was performed to obtain a soluble protein sample containing lysine decarboxylase. The amount of diaminopentane produced was increased by the catalytic reaction of lysine decarboxylase. BP coloring agent can be detected at a wavelength of 595 nm. The reaction conditions listed in Table 1 below were used to measure the activity of lysine decarboxylase. The enzyme activity can be calculated by conversion between the wavelength difference of 595 nm (Δ OD₅₉₅) and the calibration curve of diaminopentane quantified by HPLC.

TABLE 1

Reaction conditions of the assay for measuring
the activity of lysine decarboxylase

	Item	Concentration

Lysine

	40	mM
	Pyridoxal-5′-phosphate	0.2	mM

	BP coloring agent	1/20
	Sample to be tested	1/20
	Sodium acetate buffer, pH = 6

	Total volume	500	μL

As shown in FIG. 5, an inducer was not needed to be added for producing CadA during culture of JCadA/W3110, such that the biomass of JCadA/W3110 was higher than that of the inducible strain at the same time. As to the activity of CadA measured by the BP assay, the results showed that JCadA/W3110, after 30 hours of fermentation, still retained CadA activity above 150 g_DAP/g_DCW/h (i.e., specific activity), which was even 2 times higher than that of the inducible strain.

Example 6: Plasmid Stability Test

In order to test the stability of plasmids, the transformed strain JCadA/W3110 was subcultured. For the subculture, the strain stocked at −80° C. was inoculated into the medium. After 12 hours of culture, the strain was diluted and coated on the plate medium for activation, indicating as generation 0. Next, a single colony was selected from this activated plate medium and inoculated into the medium; after 12 hours of culture, the strain was diluted and coated on the plate medium, indicating as generation 1. After that, a single colony was selected from the generation 0 plate medium and inoculated into the medium every 7 days for 1 month.
The cells cultured for 12 hours were washed twice with sterilized water, concentrated to a certain OD value, and then heated in a 100° C. water bath for 10 minutes to lyse the cells. After centrifuging at the highest speed for 10 minutes, the cell pellet and substances dissolved from cells were separated. The plasmid copy number was determined by qPCR (quantitative PCR).
FIG. 6A shows that the colonies activated for 2 weeks can reach the maximum copy number. After 2 weeks, the copy number showed a downward trend. After 1 month of activation, the copy number remained slightly higher than the initial copy number. In addition, FIG. 6B and Table 2 below showed that the protein expression after 2 weeks of activation had a downward trend. From these results, it can be seen that although the copy number of this plasmid has decreased, it can still maintain stable performance.

TABLE 2

Quantitative analysis of protein performance

	Time (days)	Relative amount

	0	1.00
	7	0.32
	14	0.43
	28	0.77

In addition, the transformed strain JCadA/W3110 was cultured in a medium supplemented with antibiotics, and subjected to the stability test under different resistance concentrations. For the resistance culture, the strain stocked at −80° C. was inoculated into the medium as a pre-culture, and then 1% of the pre-culture liquid was inoculated into a 4 mL culture tube. Different concentrations (0, 5, 10 and 25 ppm) of chloramphenicol were added in sequence. The mixtures were incubated in an incubator at 37° C. for 12 hours, and 1 to 2 mL of bacterial solutions were collected for analysis.
As shown in FIGS. 6C and 6D and Table 3 below, the strains grown at different chloramphenicol concentrations maintained a certain plasmid copy number. The protein expression levels were also maintained, even under the environment without resistance. It thus can be seen that the plasmid can be stably present in the JCadA/W3110 strain.

TABLE 3

Quantitative analysis of protein performance

	Concentration (ppm)	Relative amount

	0	1.00
	5	1.11
	10	1.38
	25	2.16

Example 7: Comparison of Scale-Up Production

In this example, the whole-cell biocatalyst JCadA/W3110 was produced under three culture strategies, i.e., an Erlenmeyer flask, a fermentation tank and a high-density fermentation tank, and the bacterial number and activity were analyzed. The number of bacteria was represented as OD value, which was measured with a spectrophotometer at a wavelength of 600 nm, and the activity of lysine decarboxylase was measured by BP assay. The composition and culture conditions of the medium were shown in Tables 4 and 5 below.

TABLE 4

Medium composition for test

	Medium composition	g/L

	Glucose	20
	(NH₄)₂ HPO ₄	3
	KH₂PO₄	7
	Citric acid	0.8
	MgSO₄•7H₂O	1
	Yeast extract	2
	Chloramphenicol	0.025
	Trace metal solution
	FeSO₄•7H₂O	0.03
	ZnSO₄•7H₂O	0.00675
	CuSO₄•5H₂O	0.003
	MnSO₄•5H₂O	0.0015
	Na₂B₄O₇•10H₂O	0.00069
	CaCl₂•2H₂O	0.00405
	(NH₄)₆Mo₇O₂₄•4H₂O	0.0003

TABLE 5

Culture conditions

Erlenmeyer flask	Fermentation tank	High-density fermentation
culture	culture	tank culture

Container

250 mL Erlenmeyer	5 L stirred fermentation tank	5 L stirred fermentation tank
Erlenmeyer flask	(FB-6S, FIRSTEK, Taiwan)	(FB-6S, FIRSTEK, Taiwan)
(SCHOTT DURAN, Germany)

Action volume

50

mL

3

L

3

L

Inoculation liquid	1:100	1:100	1:100
volume ratio
pH	No pH control	pH 6.8	pH 6.8

Dissolved	—	3	L/min	3	L/min
Oxygen (DO)

Temperature

32°

C.

32°

C.

32°

C.

Rotation speed

100

rpm

100 to 1000 rpm

Feed			Glucose: 418 g/L
composition			MgSO₄•7H₂O: 15 g/L
			Yeast extract: 50 g/L
			Chloramphenicol: 0.025 g/L
Feed flow rate			0.5 to 1 mL/min

FIG. 7 showed the yield and activity status of whole-cell biocatalysts produced by the three culture strategies. The quantitative data were also shown in Table 6 below. From these results, it can be seen that, compared with Erlenmeyer flasks and fermentation tanks, culture using high-density fermentation tanks not only increases the amount of bacteria, but also increases the activity per unit of bacteria. Specifically, the use of high-density fermentation can largely increase the amount of bacteria, and produce 30 g/L of lysine decarboxylase with an activity of 170 U/mg/hour, which is useful in preparation of 1,5-diaminopentane whole-cell biocatalyst with high lysine decarboxylase activity.

TABLE 6

Yield of whole-cell biocatalyst produced
by different culture methods

Erlenmeyer	Fermentation	High-density
flask	tank	fermentation tank

OD₆₀₀	4.35	24.4	134
Specific activity	116	167	169
(g_DAP/g_DCW/h)
Total activity	167	1345	7473
(g_DAP/h)

Example 8: Test for Degradation Rate of Activity after Cryopreservation

The whole-cell biocatalyst JCadA/W3110 produced by the fermentation tank was stoked at −80° C. and taken out for culture on Day 20 and Day 130, and the activity state thereof was tested. When thawing, the bacterial mass was quantified with OD value and subjected to disruption, and the activity thereof was measured by BP assay.
FIG. 8 showed that after 20 days of cryopreservation, JCadA/W3110 still had the same CadA activity as that before the cryopreservation. Furthermore, after 130 days of cryopreservation, it still had about half of the enzyme activity, and contained 95% of the remaining activity related to the inducible strain. It can be seen that the lysine decarboxylase expressed by W3110 using the non-inducible expression system does have the effects of high protein expression, high enzyme activity and slow degradation rate.
The above-mentioned embodiments are only illustrative and not intended to limit the present disclosure. Those skilled in the art can modify and change the above embodiments without departing from the scope of the present disclosure. Therefore, the scope of protection of the rights of the present disclosure is defined by the attached claims. As long as it does not affect the effects and implementation purposes of the present disclosure, it should be encompassed in the technical content of this disclosure.

REFERENCES

[1] Z. G. Qian, X. X. Xia, S. Y. Lee (2011) Metabolic engineering of Escherichia coli for the production of cadaverine: a five carbon diamine. Biotechnology and Bioengineering, 108(1), 93-103.
[2] D. H. Kwak, H. G. Lim, J. Yang, S. W. Seo, G. Y. Jung (2017) Synthetic redesign of Escherichia coli for cadaverine production from galactose. Biotechnology for Biofuels, 10(1), 20.
[3] J. Wang, X. Lu, H. Ying, W. Ma, S. Xu, X. Wang, K. Chen, P. Ouyang (2018) A novel process for cadaverine bio-production using a consortium of two engineered Escherichia coli. Frontiers in Microbiology, 9, 1312.
[4] W. C. Ma, W. J. Cao, H. Zhang, K. Q. Chen, Y. Li, P. K. Ouyang (2015) Enhanced cadaverine production from L-lysine using recombinant Escherichia coli co-overexpressing CadA and CadB. Biotechnol. Lett., 37, 799-806.
[5] H. J. Kim, Y. H. Kim, J. H. Shin, S. K. Bhatia, G. Sathiyanarayanan, H. M. Seo, K. Y. Choi, Y. H. Yang, K. Park (2015) Optimization of direct lysine decarboxylase biotransformation for cadaverine production with whole-cell biocatalysts at high lysine concentration, J. Microbiol. Biotechnol., 25, 1108-1113.
[6] W. C. Ma, K. Q. Chen, Y. Li, N. Hao, X. Wang, P. K. Ouyang (2017) Advances in cadaverine bacterial production and its applications, Engineering, 3, 308-317.

Claims

What is claimed is:

1. An expression vector, comprising a nucleotide sequence for encoding lysine decarboxylase CadA and a sequence of a constitutive promoter for regulating expression of the nucleotide sequence.

2. The expression vector of claim 1, wherein the nucleotide sequence for encoding lysine decarboxylase CadA is a sequence having at least 80% identity to SEQ ID NO: 1 and having a same activity as SEQ ID NO: 1.

3. The expression vector of claim 1, wherein the nucleotide sequence for encoding lysine decarboxylase CadA is SEQ ID NO: 1.

4. The expression vector of claim 1, wherein the constitutive promoter is one of J series constitutive promoters.

5. The expression vector of claim 4, wherein the constitutive promoter is J23100, J23109 or J23114.

6. A recombinant microorganism for producing 1,5-diaminopentane, comprising the expression vector of claim 1.

7. The recombinant microorganism of claim 6, which is genus Escherichia, Klebsiella, Erwinia, Serratia, Providencia, Corynebacterium or Brevibacterium.

8. The recombinant microorganism of claim 6, which is recombinant Escherichia coli strain K-12 W3110.

9. The recombinant microorganism of claim 6, which is Escherichia coli W3110-JcadA deposited at Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures under DSMZ Accession No. DSM 33576.

10. A method for producing 1,5-diaminopentane, comprising:

mixing the recombinant microorganism of claim 6 with lysine in a solution to convert the lysine to the 1,5-diaminopentane; and

recovering the 1,5-diaminopentane from the solution.

11. The method of claim 10, further comprising culturing the recombinant microorganism by high-density fermentation before being mixed with the lysine in the solution.

12. The method of claim 10, further comprising adding a cofactor to the solution.

13. The method of claim 12, wherein the cofactor is pyridoxal-5′-phosphate.